The gist of this invention is the measurement of unknown signal levels. The unknown signal is converted into a pulse train the periodicity of which is proportional to signal strength. Usually, a more rapid pulse rate is keynote to a higher signal level.
In earlier art, an unknown signal is rectified and the resulting d.c. value is coupled with a voltage controlled oscillator. The result is a pulse signal having a periodicity which is varied relative to signal strength. Such a detector arrangement is taught by Weber in U.S. Pat. No. 4,044,299. The disadvantage is that the resultant pulse rate is only an indirect measure of signal level.
Further improvement is had in Weber U.S. Pat. No. 4,137,500 which teaches an exciter which produces a frequency dependent amplitude modulated signal which has an inherent modulation character which provides a step pattern pulse train signal which may cooperate with the translator taught in Weber U.S. Pat. No. 4,147,973. The translator is arranged so as to respond to the individual amplitude steps of the pulse train produced by the separate exciter. The result is a detector which recovers a sequence of component pulse rates, the periodicity of which is dependent on the signal level received from the exciter.
The instant invention improves upon this earlier art in that the advantage of signal value related pulse level detection, e.g. frequency dependent amplitude modulated signal detection, is provided while retaining the use of a conventional steady signal source. Therefore, pre-existing signal sources, such as ordinarilly used in telecommunications and the like, serve to provide the necessary input signal to this invention.